In modern oceans, the calcareous skeletons of plankton are characterized by positive δ 13 C values because the dissolved bicarbonate in surface seawater is relatively depleted in carbon-12, a consequence of the preferential utilization of the lighter isotope during photosynthesis. At the K/T boundary, the gradient collapsed to zero, or a reversed gradient was temporarily established. The breakdown of the gradient is a manifestation of greatly reduced biomass production in the strangelove ocean after the terminal Cretaceous catastrophe (Hsü and McKenzie, 1985). In addition, we propose that the reversed gradient is possibly characteristic of an ocean in which a bacterial respiration control on the surface-water δ 13 C dominated over photosynthesis (McKenzie and others, 1989). We further suggest that the very large negative δ 13 C values across the K/T, Permian/Triassic, and Precambrian/Cambrian boundaries are evidence of “respiring oceans” after global catastrophes at era boundaries. The origins of strangelove (zero-gradient) and respiring (negative gradient) oceans are related to reduced biomass productions after global catastrophes. Either an impact by a very large bolide or by explosive volcanism could be the ultimate cause of such catastrophes. From what we know now, however, the latter happened too frequently in geologic history to account for the rare era-boundary events.

In many parts of the world a thin clay or marly unit marks the boundary between Cretaceous and Tertiary rocks. In marine sequences this boundary is defined by the first appearance of typically Paleocene marine plankton in the clay. In continental rocks, the boundary sediment yields the stratigraphically highest occurrence of a Cretaceous assemblage of fossil pollen. Detailed analyses of the marine boundary sediment at Caravaca, Spain, permit a three-fold subdivision: the lowest is apparently a fallout deposit of impact ejecta, preserved as a 0.5-cm lamina of red clay. The main subdivision is a black or dark gray clay or marl, containing reworked extraterrestrial debris, laid down in an oxygen-deficient environment. The uppermost boundary clay is lighter gray in color, transitional in lithology to the overlying Paleocene sediments, which were deposited after the recovery from the terminal Cretaceous convulsive event. The boundary clay unit on land, represented by a section in Raton Basin, New Mexico, consists of a lower white clay, which is apparently a fallout deposit, and an upper carbonaceous shale. Boundary sections elsewhere are similar to those sections. The sedimentology of the boundary sediment records the convulsive environmental changes at/after a terminal Cretaceous event.

Abstract The Franciscan of the California Coast Ranges was considered a lithostratigraphic unit (a formation or group of formations) for more than a century. Normal stratigraphical methodology was practised, and few questioned the applicability of the laws of superposition, lateral continuity, and paleontological dating. Despite evidence to the contrary, researchers portrayed deformation of coherent strata. Metamorphic conditions were deduced on the basis of presumed field relations, and the geosynclinal theory of mountain building was the paradigm. A subjective choice of data allowed researchers to fit the Franciscan into a straight-jacket, and for many years it was described as a Late Jurassic Tithonian formation, deposited in a eugeosyncline on the western margin of the North American continent after the Nevadan Orogeny. The classical model failed to take into account a number of key observations that challenged accepted beliefs. Micropaleontological evidence for the Cretaceous age of some Franciscan rocks was known but not taken seriously. Finally, however, the discovery of an ammonite of undoubted Cretaceous age in a Franciscan sandstone at the type locality led to a crisis. It became impossible to ignore mounting evidence that the Franciscan contains rocks coeval to the Great Valley Sequence, which ranges in age from Tithonian to Late Cretaceous, despite the fact that rocks of typical Franciscan lithology (e.g., ophiolites) underlie the Knoxville and should therefore be older than the Great Valley Sequence. The application of the mélange concept and the assumption of underthrusting resolved the Franciscan-Knoxville Paradox, and resulted in a revolutionary change in our thinking on Franciscan geology. At about the same time, a new paradigm in geology, the new plate-tectonic theory, was introduced. With plate tectonics, crises could be overcome, contradictions eliminated, and a period of “normal science” could prevail. Franciscan research went through five stages: 1) random observations; 2) synthesis; 3) crisis; 4) revolution, or overthrow of the old paradigm and establishment of the new; and 5) mopping up. A history of the process illustrates the theory of scientific revolution advocated by Thomas Kuhn.

Significant changes of the chemistry, temperatures, and plankton fertility in the oceans took place in the first fifty thousand years of the Tertiary. Those changes are recorded by the bulk chemical, the oxygen-isotope, and the carbon-isotope compositions of the oldest Tertiary sediments. Detailed analyses of a Cretaceous/Tertiary section from a South Atlantic drillsite indicated that the extinction of the Cretaceous nannoplankton species took place during the times of the environmental changes. Taking into consideration the various evidences for a terminal Cretaceous large-body impact, we proposed that the impact event was the cause of the changes in ocean environments, which in turn led to the rapid extinction of marine plankton species.

Abstract The hydrology and geochemistry of subsurface waters from a Holocene area of dolomitization, the coastal sabkhas of Abu Dhabi, have been investigated. The origins of the waters (lagoon, open marine, continental and mixed) were defined by their K: Br ratios and stable isotope values. Downward movement of Hood recharge waters was established by decreasing tritium contents with depth under the sabkha. Further, evaporation from the capillary zone imprinted a distinctive δD ratio upon waters from the intermediate sabkha. Measurements established the hydrologie framework under the sabkha. Two aquicludes separate the near surface sediments from the underlying aquifers. The presence of these aquicludes enabled us to measure vertical hydrauuc gradients. The gradient is locally directed downward for a short time after supratidal flooding, but for the most part is directed upward, especially in the area of Holocene dolomitization. Together, the data were synthesized into a hydrologie model for the intermediate sabkha, the area where dolomitization occurs. A single hydrologie cycle was defmed by three sequential stages; flood recharge, capillary evaporation and “evaporative pumping.” The processes involved in the evolution of a dolomitizing solution and the driving forces required to move the solutions through the sediments being dolomitized are inherent in the model.

Three important Alpine pelagic lithologic types are ammonitico rosso, Radiolarite, and Maiolica, which range in age from late Early Jurassic to Early Cretaceous. Ammonitico rosso is in many places red nodular limestone, lying above continental crust. This pelagic deposit bears some resemblance to some Holocene nodular deposits in the eastern Mediterranean. A somewhat restricted Middle Jurassic Alpine Tethys sea has been postulated to account for the occurrence of the “home-made” bottom currents that led to partial dissolution of aragonite and precipitation of calcite nodules. The sudden appearance of the radiolarite facies in Late Jurassic time may signify a major tectonic event that sufficiently altered the Tethyan paleogeography to permit the intrusion of an equatorial current into the Alpine realm. The radiolarite facies is commonly believed to have been deposited beneath the calcite compensation depth, but calcitic aptychi have been found in radiolarite, and Aptychus Limestone is intimately associated with this mainly siliceous formation. The depths of the Radiolarite sea during Late Jurassic time were probably closer to the lysocline for aragonite. Because the Radiolarite is the first sediment deposited on ophiolite, one might postulate that the Tethys at the time of Radiolarite deposition had an oceanic depth comparable to that in regions of newly formed crust. Both lines of reasoning have led me to suggest that the Tethys in Late Jurassic time had a depth of 2,500 ± 200 m, not 4,000 to 5,500 m as postulated previously by some authors. The Maiolica Formation is pelagic limestone with slump interbeds and intraformational chert nodules. The radiolarite-limestone succession in the Alpine Tethys is exactly the opposite of the simple model constructed by plate stratigraphers, who usually found a limestone-radiolarite-red clay succession on an aging crust. It is possible that excessive blooms of siliceous faunas may have created a silica crisis at the end of Jurassic time. The Alpine Tethys, being disadvantageously situated at the end of the Jurassic equatorial current system, could no longer be given enough silica to produce radiolarians. In their place, a calcareous flora of nannofossils flourished, resulting in the change from Radiolarite sedimentation to Maiolica sedimentation. Considering the rate of the silica transport, chert in the Maiolica deposit could not have been formed by submarine diagenesis. Nodules took millions of years to grow in formations in which concentration gradients existed between the domain where amorphous biogenic silica was being dissolved and the nuclei around which quartz or cristobalite was being precipitated.